Lamp base



FIG. 1 is a perspective view of lamp base showing my new design;

FIG. 2 is a front elevation view thereof, the rear, the left and the right side elevation view thereof being identical in appearance;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a bottom plan view thereof. 

The ornamental design for a lamp base, as shown and described. 